drm/nouveau/gr/gf100-: lose contents of global ctxbufs across suspend

Some of these buffers are quite large, and there's no need to preserve
them across suspend.

Mark the contents as lost to speedup suspend/resume.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Acked-by: Danilo Krummrich <me@dakr.org>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230919220442.202488-4-lyude@redhat.com